1. Field of the Invention
The present invention generally relates to magnetic recording mediums and magnetic storage apparatuses, and more particularly to a magnetic recording medium and a magnetic storage apparatus which are suited for high-density recording.
2. Description of the Related Art
The recording density of longitudinal magnetic recording media, such as magnetic disks, has been increased considerably, due to the reduction of media noise and the development of magnetoresistive and high-sensitivity spin-valve heads. Recording densities above 20 Gb/in2 have recently been demonstrated for the magnetic disks. The demand for greater recording densities for better performing computers is however showing an increasing trend imposing greater challenges for the recording media and other component design.
FIG. 1 is a cross sectional view showing an important part of a typical longitudinal magnetic recording medium. The magnetic recording medium is comprised of a substrate 1, a Cr or Cr-based underlayer 2, a Co-based magnetic layer 3 where information is written, and a C or DLC overlayer 4 which are stacked as shown in FIG. 1. An organic lubricant is coated on the overlayer 4.
Lowering the medium noise involves writing sharper magnetic transitions in the magnetic layer 3. This is generally achieved by increasing the media coercivity, decreasing the thickness of the magnetic layer 3, decreasing the grain size and grain size distribution of the magnetic layer 3, and magnetically isolating the grains of the magnetic layer 3. However, as the grains of the magnetic layer 3 are made smaller and magnetically isolated, the magnetic recording medium is exposed to several thermally related obstacles.
One of the thermally related obstacles is the increase in the temperature coefficient of coercivity or, a large spread in the coercivity within the operating temperature range of the magnetic recording medium. In the case of a hard disk drive, the operating temperature range is normally 5 to 65xc2x0 C., but is 0 to 100xc2x0 C. in extreme cases.
The media thickness has been decreasing over the years in order to achieve higher recording densities. Such a decrease in the media thickness was necessary to lower the media noise. Hence, with this trend, the media thickness requirement could be less than 15 nm for a magnetic recording medium having the recording density of 40 Gb/in2.
However, as shown in FIG. 2, the coercivity of the magnetic recording medium shows a large spread over the operating temperature range as the media thickness decreases. For a magnetic recording medium having a media thickness of 13 nm, the coercivity changes by about 1400 Oe for a temperature change of 0 to 100xc2x0 C. This large spread of the coercivity over the operating temperature range puts severe limitations on the media design. In other words, the overwrite performance deteriorates at low temperatures, and the media noise increases at high temperatures.
One of the requirements for achieving the high-density recording is to employ a high media coercivity. However, a large write current is required in order to write information on a magnetic recording medium having the high media coercivity. Write currents which can be produced by existing write heads are severely limited for the media coercivities higher than 3000 Oe, because the development of high magnetic moment write heads has been slow.
The difficulty in writing the information on the magnetic recording medium having the high media coercivity is normally referred to in terms of the overwrite performance. A large variation of the coercivity leads to a higher coercivity at lower temperatures of 0 to 5xc2x0 C., for example, thereby making it more difficult to obtain a satisfactory overwrite performance. The magnetic recording mediums having the recording densities above 20 Gb/in2 are expected to have severe overwrite requirements, and any decrease in the overwrite performance at the lower temperatures will result in a major limitation for designing high-performance magnetic recording media.
Furthermore, a large variation of the coercivity also leads to a lower coercivity at higher temperatures. This decrease in the coercivity will lead to increased media noise, that is, a decrease in media signal-to-noise ratio (SNR). FIG. 3 is a diagram showing a trend in decreasing media SNR with decreasing coercivity. A variation of the coercivity over 1000 Oe per 100xc2x0 C. (1000 Oe/100xc2x0 C.) limits the design of the magnetic recording medium in terms of non-uniform media SNR over the operating temperature range.
As described above, it is desirable to reduce the coercivity spread over the operating temperature range of the magnetic recording medium. However, on the contrary, there was a problem in that physical considerations of the high-density magnetic recording media result in increasing the coercivity spread over the operating temperature range of the magnetic recording media.
Accordingly, it is a general object of the present invention to provide a novel and useful magnetic recording medium and magnetic storage apparatus, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide a magnetic recording medium and magnetic storage apparatus which have a small temperature coefficient of coercivity and low media noise over a relatively wide operating temperature range.
Still another object of the present invention is to provide a magnetic recording medium comprising a non-magnetic underlayer, and a magnetic layer including a compensation layer provided on said non-magnetic underlayer, and a recording layer provided on the compensation layer, where the compensation layer has a thickness of 3 to 15 nm and is made of Co or a Co-based alloy with a Curie temperature of approximately 30 to 150xc2x0 C., and the recording layer has a thickness of 10 to 30 nm and is made of a Co-based alloy with a Curie temperature of approximately 250 to 800xc2x0 C. According to the magnetic recording medium of the present invention, it is possible to realize a magnetic recording medium having a small temperature coefficient of coercivity and low media noise over a relatively wide operating temperature range.
A further object of the present invention is to provide a magnetic recording medium comprising a non-magnetic underlayer, and a magnetic layer including a first compensation layer provided on the non-magnetic underlayer, a second compensation layer provided on the first compensation layer and a recording layer provided on the second compensation layer, where the first compensation layer has a thickness of 1 to 5 nm and is made of Co or a Co-based alloy with a Curie temperature of approximately 0 to 50xc2x0 C., the second compensation layer has a thickness of 3 to 15 nm and is made of Co or a Co-based alloy with a Curie temperature of approximately 30 to 150xc2x0 C., and the recording layer has a thickness of 10 to 30 nm and is made of a Co-based alloy with a Curie temperature of approximately 250 to 800xc2x0 C. According to the magnetic recording medium of the present invention, it is possible to realize a magnetic recording medium having a small temperature coefficient of coercivity and low media noise over a relatively wide operating temperature range.
Another object of the present invention is to provide a magnetic storage apparatus comprising at least one magnetic recording medium having at least a non-magnetic underlayer, and a magnetic layer which includes a compensation layer provided on the non-magnetic underlayer and a recording layer provided on the compensation layer, where the compensation layer has a thickness of 3 to 15 nm and is made of Co or a Co-based alloy with a Curie temperature of approximately 30 to 150xc2x0 C., and the recording layer has a thickness of 10 to 30 nm and is made of a Co-based alloy with a Curie temperature of approximately 250 to 800xc2x0 C. According to the magnetic storage apparatus of the present invention, it is possible to realize a magnetic storage apparatus having a small temperature coefficient of coercivity and low media noise over a relatively wide operating temperature range.
Still another object of the present invention is to provide a magnetic storage apparatus comprising at least one magnetic recording medium having at least a non-magnetic underlayer, and a magnetic layer which includes a first compensation layer provided on the non-magnetic underlayer, a second compensation layer provided on the first compensation layer and a recording layer provided on the second compensation layer, where the first compensation layer has a thickness of 1 to 5 nm and is made of Co or a Co-based alloy with a Curie temperature of approximately 0 to 50xc2x0 C., the second compensation layer has a thickness of 3 to 15 nm and is made of Co or a Co-based alloy with a Curie temperature of approximately 30 to 150xc2x0 C., and the recording layer has a thickness of 10 to 30 nm and is made of a Co-based alloy with a Curie temperature of approximately 250 to 800xc2x0 C. According to the magnetic storage apparatus of the present invention, it is possible to realize a magnetic storage apparatus having a small temperature coefficient of coercivity and low media noise over a relatively wide operating temperature range.
Other objects and further features of the present invention may be apparent from the following detailed description when read in conjunction with the accompanying drawings.